Mass Accretion During the Motion of Raindrops

Exploration of dynamics of raindrops is one of the simple yet most complicated mechanical problems. Mass accretion from moist air during the motion of raindrop through resistive medium holds an arbitrary power law equation. Its integral part is the change of shape, terminal motions and terminal solutions, etc. Classical Newtonian formalism is used to formulate a mathematical model of generalized first order differential equation. We have discussed about the terminal velocity of raindrop and its variation with the extensive use of python program and library. It is found that terminal velocity 𝐯𝐓𝐜𝛂𝛃 is achieved within 20 seconds where 𝛂=, 𝛃=(𝟎,𝟏) and 𝐧=𝟎,𝟏,𝟐,𝟑,𝟒,…. Its variations due to mass accretion roughly follows the earlier predicted range 𝐠/𝟕 to 𝐠/𝟑.

A Comprehensive Study of Mass Accretion and Atmospheric Effect of Raindrop

The mass accretion of a raindrop in different layers of the atmosphere is not dealt with so far. A comprehensive brief study of the motion of raindrops through the atmosphere (i) without mass accretion, (ii) with mass accretion and (iii) finally pressure variation in the atmosphere with altitude using Bernoulli’s equation is illustrated. Acquirement of mass from moist air is mass accretion and mass accretion during the motion of raindrop through resistive medium holds an arbitrary power-law equation. Bernoulli’s equation when applied to it, the generalized first-order differential equation is reduced to a polynomial equation. Results show a single intersecting point of approximate terminal velocity 1 m/s and mass 10-06 mg as illustrated. Terminal velocity is achieved within 25 sec. There is the approximate exponential growth of terminal velocity. An increase in momentum is due to mass accretion during motion. Various conditions of no mass accretion and mass accretion show the same result while for atmospheric effect using Bernoulli’s equation the first-order differential equation reduces to a polynomial equation.

Plant canopy may promote seed dispersal by wind

Seed dispersal has received much research attention. The plant canopy can intercept diaspores, but the effect of the plant canopy (the aboveground portion of a plant consisting of branches and leaves) on dispersal distance has not been explored empirically. To determine the effect of plant canopy on seed dispersal distance, a comparison of diaspores falling through open air and through plant canopy was made in a wind tunnel using three wind speeds and diaspores with various traits. Compared with diaspores falling through open air, the dispersal distance of diaspores falling through plant canopy was decreased or increased, depending on wind speed and diaspore traits. When falling through a plant canopy, dispersal distance of diaspores with thorns or those without appendages was promoted at low wind speed (2 m s−1), while that of diaspores with low wing loading (0.5 mg mm−2) and terminal velocity (2.5 m s−1) was promoted by relatively high (6 m s−1) wind speed. A plant canopy could increase seed dispersal distance, which may be due to the complicated updraft generated by canopy. The effect of maternal plants on seed dispersal regulates the distribution pattern and the species composition of the community.

Development of a Millet Destoner for Small Scale Farmers

Post-harvest processes of millet rely on labour-intensive manual operations in Nigeria while its produce is associated with contaminants. A manually-operated destoner was developed to increase grain value for commercial production and reduce drudgery. To construct the destoner sieves, physical properties of one thousand randomly selected grains were determined digital Vernier callipers. Millet grains to be destoned was fed through the upper portion of the destoner being operated through the crank handle while the pure grains were collected at the discharge outlet. Results obtained shows the geometric diameter of the grains increase progressively from 3.51-4.22mm as moisture content increases. A screen aperture of 3.5mm was constructed. Grains’ surface area, volume and sphericity increased from 22.67-34.82mm², 8.19-13.98mm³ and 0.691-0.776g respectively. Mass, true density and terminal velocity of 1000 seed increased from 13.56-43.84g, 1548.91-1689.87kg/m³ and 2.69-4.58m/s respectively. The bulk density of millet also increased as moisture content increases but decreased beyond 12.5% moisture level indicating that millet floats on water and was transpoted with the aid of an auger. About 50kg of millet was poured into the destoner to occupy its ⅓ capacity while the remaining ⅔ was filled with water. Destoner output was at 95% efficiency.Key words: Destoner, Millet, Processing, Properties, Contaminants

Current-Driven Domain Wall Motion in Curved Ferrimagnetic Strips Above and Below the Angular Momentum Compensation

Current driven domain wall motion in curved Heavy Metal/Ferrimagnetic/Oxide multilayer strips is investigated using systematic micromagnetic simulations which account for spin-orbit coupling phenomena. Domain wall velocity and characteristic relaxation times are studied as functions of the geometry, curvature and width of the strip, at and out of the angular momentum compensation. Results show that domain walls can propagate faster and without a significant distortion in such strips in contrast to their ferromagnetic counterparts. Using an artificial system based on a straight strip with an equivalent current density distribution, we can discern its influence on the wall terminal velocity, as part of a more general geometrical influence due to the curved shape. Curved and narrow ferrimagnetic strips are promising candidates for designing high speed and fast response spintronic circuitry based on current-driven domain wall motion.

Improving the representation of aggregation in a two-moment microphysical scheme with statistics of multi-frequency Doppler radar observations

Aggregation is a key microphysical process for the formation of precipitable ice particles. Its theoretical description involves many parameters and dependencies among different variables that are either insufficiently understood or difficult to accurately represent in bulk microphysics schemes. Previous studies have demonstrated the valuable information content of multi-frequency Doppler radar observations to characterize aggregation with respect to environmental parameters such as temperature. Comparisons with model simulations can reveal discrepancies, but the main challenge is to identify the most critical parameters in the aggregation parameterization, which can then be improved by using the observations as constraints. In this study, we systematically investigate the sensitivity of physical variables, such as number and mass density, as well as the forward-simulated multi-frequency and Doppler radar observables, to different parameters in a two-moment microphysics scheme. Our approach includes modifying key aggregation parameters such as the sticking efficiency or the shape of the size distribution. We also revise and test the impact of changing functional relationships (e.g., the terminal velocity–size relation) and underlying assumptions (e.g., the definition of the aggregation kernel). We test the sensitivity of the various components first in a single-column “snowshaft” model, which allows fast and efficient identification of the parameter combination optimally matching the observations. We find that particle properties, definition of the aggregation kernel, and size distribution width prove to be most important, while the sticking efficiency and the cloud ice habit have less influence. The setting which optimally matches the observations is then implemented in a 3D model using the identical scheme setup. Rerunning the 3D model with the new scheme setup for a multi-week period revealed that the large overestimation of aggregate size and terminal velocity in the model could be substantially reduced. The method presented is expected to be applicable to constrain other ice microphysical processes or to evaluate and improve other schemes.

Mass Exchange of Water and Soil on the Soil Surface in the Rainfall Splash Erosion

This research aims to unfold the mass exchange mechanism of water and soil on the soil surface in the rainfall splash erosion process. We regard the rainfall splash erosion process as a collision process between the raindrop and the soil particle on the soil interface. This recognition allows us to incorporate research approaches from the spring vibrator model, which has been developed for simulating the impact of liquid drops on solid surface. We further argue that because a same set of factors determine the splash amount and infiltration amount and it is relatively simpler to observe the infiltration amount, an investigation into the relationship between the splash amount and infiltration amount would be able to provide a new channel for quantifying the splash erosion. This recognition leads us to examining the relationship between single raindrop, rainfall kinetic energy and splash erosion from both theoretical and empirical angles, with an emphasis on the relationship between the infiltration amount and the splash erosion. Such an investigation would add value to the collective effort to establish mass exchange law in water-soil interface during rainfall splash erosion. It is found that during the rainfall splash process, the splash erosion is proportional to the rainfall kinetic energy; and has a linear relation to the infiltration amount, with the rainfall intensity as one of important parameters and the slope depending on the unit conversation of the infiltration amount and the splash erosion. If the units of two items are same, the slope is the ratio of the soil and water density, and the splash erosion velocity of the rainfall is half of the rainfall terminal velocity. The single raindrop kinetic energy and the splash erosion have a quadratic parabola relation, and the splash velocity is about 1/3 of single raindrop terminal velocity.